Three-Dimensional (“3D”) printing is an additive manufacturing process in which successive layers of material are formed over one another to form a 3D object. Each layer adheres to the layer below to create an integrally formed object. Various types of 3D printing process have been developed, including extrusion-based 3D printing (e.g., fused deposition modeling (FDM)), and processes based on light polymerization, such as stereolithography (SLA) and digital light processing (DLP), among others.
In stereolithography processes, a 3D structure is built up one layer at a time. Each layer is formed by exposing a photo-reactive resin to an ultraviolet (UV) light source that cures the resin. Note that stereolithography may also be referred to as optical fabrication, photo-solidification, and/or solid free-form fabrication and solid imaging.
In a typical stereolithography process, a digital 3D model of an object is created by a user using a software application that interfaces with the 3D printing system. The application determines a set of layers that correspond to the object. The layers can be determined by thin slices through the 3D model with a set of horizontal planes. Each slice of the 3D model can then be converted to a two-dimensional mask pattern, such that the 3D model is represented as a sequence of two-dimensional mask patterns, which each outline the shape of the corresponding layer from the 3D model. The mask patterns can be sequentially projected onto a photo-reactive liquid or powder resin surface while the resin is illuminated with UV light to cure the resin not shielded by the mask in the shape of the corresponding layer. Alternatively, instead of using masks, each slice of the 3D model may be representing by a two-dimensional pattern in the shape of the slice, so that a projector or other imaging system can illuminate a sequence of such patterns onto the resin to form the object.